Exoplanet Update and GLAST News

by Paul Gilster on May 30, 2008

Following up on yesterday’s post on EPOCh, the extended exoplanet mission of the Deep Impact spacecraft, I want to mention that principal investigator Drake Deming (NASA GSFC) will be in my old home town of St. Louis on June 2 as part of the 212th meeting of the American Astronomical Society. Deming will be giving an update on the search for ‘super Earths’ of the sort that EPOCh may be able to spot during its investigations, while David Bennett (Notre Dame) as well as Michael Liu and Trent Dupuy (University of Hawaii) will be discussing other developments related to the exoplanet hunt and the study of brown dwarfs. We’ll keep an eye out for EPOCh results, particularly re GJ 436.

Also of relevance to future exoplanet as well as other astronomical studies is an upcoming report by Paul Chen (Catholic University) on work at NASA Goddard on inexpensive ways to make giant telescope mirrors on the Moon. That session will take place at the AAS on June 4 under the heading ‘Speculative Astrophysics,’ and speculative as it may be, the physics behind creating such mirrors seems feasible. What’s problematic is the engineering and, of course, the commitment to create and expand a serious scientific base on the Moon. Still, the mind turns to Claudio Maccone’s studies of dark side observatories free of Earthly interference and the possibilities become dazzling.

And finally, the GLAST (Gamma-Ray Large Area Space Telescope) mission, so potentially useful in the study of gamma-ray bursts (GRBs), is now closing on a June 5 launch, the window being from 1545 to 1740 UTC (remaining open through August 7). NASA TV will have launch commentary beginning at 1345. Among GLAST’s exciting possibilities (recently discussed here) is detecting the signature of WIMPs (weakly interacting massive particles), the leading candidate for dark matter. The latter, if indeed composed of WIMPs, may release a continuing stream of gamma rays and secondary particles that would contrast sharply with the abrupt GRBs that are under such active scrutiny.

Image: The first half of the payload fairing is moved into place around NASA’s Gamma-Ray Large Area Space Telescope within the mobile service tower on Launch Pad 17-B at Cape Canaveral Air Force Station. The fairing is a molded structure that fits flush with the outside surface of the Delta II upper stage booster and forms an aerodynamically smooth nose cone, protecting the spacecraft during launch and ascent. Credit: NASA/Jim Grossmann.

This, of course, is how science works. You study natural phenomena and create hypotheses to explain what you see (i.e., the apparent effect of ‘missing’ mass in galaxy formation and the gravitational lensing that seems to be produced by that mass). You test your models in hopes of finding the most reasonable explanation. Your predictions may agree with your hypothesis, but if they don’t, you go back to work on the original model. Gravitational lensing involving galactic clusters is widely observable (over a hundred galactic arcs have been found), but detecting the signature of WIMPs would add highly useful background data to the dark matter hunt underway in Earth-based detectors right now.

Abstract: We present quantitative predictions for the detectability of individual Galactic dark matter subhalos in gamma-rays from dark matter pair annihilations in their centers. Our method is based on a hybrid approach, employing the highest resolution numerical simulations available (including the recently completed one billion particle Via Lactea II simulation) as well as analytical models for the extrapolation beyond the simulations’ resolution limit.

We include a self-consistent treatment of subhalo boost factors, motivated by our numerical results, and a realistic treatment of the expected backgrounds that individual subhalos must outshine.

We show that for reasonable values of the dark matter particle physics parameters (M_X ~ 50 – 500 GeV and ~ 10^-26 – 10^-25 cm^3/s) GLAST may very well discover a few, even up to several dozen, such subhalos, at 5 sigma significance, and some at more than 20 sigma. We predict that the majority of luminous sources would be resolved with GLAST’s expected angular resolution. For most observer locations the angular distribution of detectable subhalos is consistent with a uniform distribution across the sky.

The brightest subhalos tend to be massive (median Vmax of 24 km/s) and therefore likely hosts of dwarf galaxies, but many subhalos with Vmax as low as 5 km/s are also visible. Typically detectable subhalos are 20 – 40 kpc from the observer, and only a small fraction are closer than 10 kpc. The total number of observable subhalos has not yet converged in our simulations, and we estimate that we may be missing up to 3/4 of all detectable subhalos.

Comments: 19 pages, 12 figures, ApJ accepted, a version with higher resolution figures can be downloaded from this http URL

WASHINGTON — NASA has set June 11 as the new no-earlier-
than target launch date for the Gamma-ray Large Area Space
Telescope, or GLAST, from Cape Canaveral Air Force Station
in Florida. The launch window extends from 11:45 a.m. to
1:40 p.m. EDT.

NASA initially had targeted June 7 for the GLAST launch aboard
a Delta II rocket. Additional time was needed to replace the
rocket’s flight termination system battery, which indicated a
problem Wednesday.

The GLAST prelaunch news conference is planned for 1 p.m.
on Monday, June 9, at NASA’s News Center at the Kennedy
Space Center. Question-and-answer capability will be available
from participating NASA locations.

Placement of remote cameras at Pad 17B is planned for 1 p.m.,
Tuesday, June 10. On launch day, news media should meet at
10:30 a.m. at the Space Florida parking lot outside Gate 1 of
Cape Canaveral Air Force Station.

NASA’s Gamma-ray Large Area Space Telescope (GLAST for short)
left Earth today onboard a Delta II rocket. “The entire GLAST Team
is elated,” reports program manager Kevin Grady of NASA’s Goddard
Space Flight Center. “The observatory is now on-orbit and all systems
continue to operate as planned.” Read today’s Science@NASA story to
learn about some of the exciting new science GLAST is expected to accomplish.

The launch of GLAST on June 11 represents an important milestone in gamma
ray astronomy. For GRB studies specifically, we look forward to unprecedented
spectral coverage. Activation of the spacecraft, the Large Area Telescope,
and the GLAST Burst Monitor has been proceeding very well. Both instruments
are now fully powered up and the teams are engaged in the fine-tuning
required for normal science operations. All of the GBM detectors are working
beautifully and we even detected a weak burst on the first day of operation.
This early success bodes well for the 2008 Huntsville Symposium. We look
forward to many stimulating presentations and discussions on gamma-ray
bursts from GLAST, Swift and other observatories in Huntsville in October.

The 6th Huntsville GRB Symposium Web page is on-line and we invite you
to register and submit your abstracts by July 31st. Please indicate at the
end of your abstract the session where you would like it presented. The list
of sessions and invited speakers is included below and can be also found at

Comparison predictions for AGILE are made. Hard ($\gg 5$ GeV) SSC or photohadronic tails on GRBs, or GRBs with anomalous hard components, could increase the rates and would define separate classes of GRBs.

Abstract: We investigate the sensitivity of the Gamma-ray Large Area Space Telescope (GLAST) to indirectly detect weakly interacting massive particles (WIMPs) through the $\gamma$-ray signal that their pair annihilation produces. WIMPs are among the favorite candidates to explain the compelling evidence that about 80% of the mass in the Universe is non-baryonic dark matter (DM). They are serendipitously motivated by various extensions of the standard model of particle physics such as Supersymmetry and Universal Extra Dimensions (UED).

With its unprecedented sensitivity and its very large energy range (20 MeV to more than 300 GeV) the main instrument on board the GLAST satellite, the Large Area Telescope (LAT), will open a new window of discovery. As our estimates show, the LAT will be able to detect an indirect DM signature for a large class of WIMP models given a cuspy profile for the DM distribution. Using the current state of the art Monte Carlo and event reconstruction software developed within the LAT collaboration, we present preliminary sensitivity studies for several possible sources inside and outside the Galaxy.

We also discuss the potential of the LAT to detect UED via the electron/positron channel. Diffuse background modeling and other background issues that will be important in setting limits or seeing a signal are presented.

Abstract: This paper analyzes astrophysical scenarios that may be detected at the upper end of the energy range of the Gamma Ray Large Area Space Telescope (GLAST), as a result of cosmic-ray (CR) diffusion in the interstellar medium (ISM). Hadronic processes are considered as the source of $\gamma$-ray photons from localized molecular enhancements nearby accelerators.

Two particular cases are presented: a) the possibility of detecting spectral energy distributions (SEDs) with maxima above 1 GeV, which may be constrained by detection or non-detection at very-high energies (VHE) with observations by ground-based Cerenkov telescopes, and b) the possibility of detecting V-shaped, inverted spectra, due to confusion of a nearby (to the line of sight) arrangement of accelerator/target scenarios with different characteristic properties.

We show that the finding of these signatures (in particular, a peak at the 1–100 GeV energy region) is indicative for an identification of the underlying mechanism producing the $\gamma$-rays that is realized by nature: which accelerator (age and relative position to the target cloud) and under which diffusion properties CR propagate.

Fitting the Gamma-Ray Spectrum from Dark Matter with DMFIT: GLAST and the Galactic Center Region

Authors: Tesla E. Jeltema, Stefano Profumo

(Submitted on 19 Aug 2008)

Abstract: We study the potential of GLAST to unveil particle dark matter properties with gamma-ray observations of the Galactic center region. We present full GLAST simulations including all gamma-ray sources known to date in a region of 4 degrees around the Galactic center, in addition to the diffuse gamma-ray background and to the dark matter signal.

We introduce DMFIT, a tool that allows one to fit gamma-ray emission from pair-annihilation of generic particle dark matter models and to extract information on the mass, normalization and annihilation branching ratios into Standard Model final states. We assess the impact and systematic effects of background modeling and theoretical priors on the reconstruction of dark matter particle properties.

Our detailed simulations demonstrate that for some well motivated supersymmetric dark matter setups with one year of GLAST data it will be possible not only to significantly detect a dark matter signal over background, but also to estimate the dark matter mass and its dominant pair-annihilation mode.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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